EGM2008 - Files & Products for Oceanographic Applications

Introduction

The official Earth Gravitational Model EGM2008 has been publicly released by the U.S. National Geospatial-Intelligence Agency (NGA) EGM Development Team. This gravitational model is complete to spherical harmonic degree and order 2159, and contains additional coefficients extending to degree 2190 and order 2159.

This page contains data files for Oceanographic Applications of EGM2008. The files include a geoid undulation grid, a Dynamic Ocean Topography (DOT) grid, and a set of spherical harmonic coefficients of the DOT. The geoid undulation values refer to the "Mean Tide" system as far as the Permanent Tide is concerned. They were computed with respect to an “IDEAL” mean-Earth ellipsoid as far as its semi-major axis is concerned. That is, the zero-degree term of the geoid undulations is set to ZERO, and the semi-major axis of this “IDEAL” ellipsoid remains numerically unspecified. However, the geoid undulations refer to an ellipsoid whose flattening is equal to:

f = 1/298.257

so that these geoid undulations are consistent with the flattening used to report Sea Surface Heights (SSH) from the TOPEX/Poseidon mission. The grids below should NOT be used for GPS/Leveling work.
If you wish to compute geoid undulations with respect to the WGS 84 Geodetic Reference System, please go to the EGM2008 - WGS 84 Version.

Filenames containing a ".gz" in the suffix have been compressed using the Unix "gzip" command.

All files that are SMALL ENDIAN format are highlighted in green. All files that are BIG ENDIAN format are highlighted in purple.

Please carefully review the OCEAN_README_FIRST file for a complete description of the data files below. Also, please read the disclaimer before using any of the data that has been made available on this page.